Method and apparatus for processing coatings, radiation curable coatings on wood, wood composite and other various substrates

Abstract

A method and apparatus that combines the coating spray booth with process heating and radiation to increase the efficiency of the processing of powder coatings on wood, wood-based composite materials and plastic substrates. The temperature of the parts in process can be maintained within the booth after preheating or elevated in temperature within the booth before, during, and after the application of the coating material. The invention allows for the control of the rate of thermal expansion of heat sensitive materials, thereby reducing substrate damage from cracking. Increased efficiencies permit a significant reduction of processing energy expense. Multiple coatings can be applied and cured to parts in process within the invention while experiencing an overall reduction in the length of the processing system compared to the prior art.

Description

[0001] The present invention relates to a method and apparatus that safely combines the coating spray booth with infrared radiant process heating to increase the efficiency of processing coatings on temperature sensitive substrates, such as wood, wood-based materials, and plastics. The terms "temperature sensitive" refers to objects that possess a low rate of thermal conductivity and / or a relatively high thermal expansion factor. The application of ultraviolet radiation can also be safely combined with the spray booth equipment for efficiently processing ultraviolet curable coatings. The invention provides a method and apparatus to safely maintain, increase and control the surface temperature of objects in process while in the spray booth before, during and after the application of the coating material upon the objects. The invention also provides a method and apparatus to safely control the coefficient of thermal expansion of the objects in order to avoid physical damage to tempera...

AI Technical Summary

Benefits of technology

0021] It should be noted that the atmosphere, including the chilled (or warm) moisture controlled fluid, does not efficiently absorb IR radiation. The cool (or warm) fluid that contains the valuable moisture for enhancing the electromagnetic attraction of the powder is not in jeopardy when applied prior to the initial IR preheat process. The IR radiation will pass freely through the cool (or warm) fluid that is lying in the grooved areas, and will be successfully absorbed by the substrate. Some heat transfer may occur from the substrate to the enhanced fluid, but primarily by thermal conduction. The heat energy transfer will be proportional to the temperatures achieved in the substrate, the temperature of the enhanced fluid, the relative humidity of the chilled (or warm) air, and the amount of time of intimate contact prior to the applic...

Problems solved by technology

Since these materials are electrically non-conductive, there are difficulties associated with the consistent earth grounding of the wood that is critical for the electrostatic spraying process.

However, this critical moisture layer is only present for a short period of time.

Further, the moisture that has risen to the target surface is in limited supply, even though significant quantities of moisture still reside within the substrate.

Therefore, the quantity of available moisture that can be rapidly driven to the surface is in very low supply.

Thin recessed areas in wood substrates pose unique moisture problems.

Exposure to dry air over time causes the thin areas to lose their moisture faster than the thick areas.

Initially, both devices will discharge the same voltage, but the larger battery will require more time to completely drain.

In time, this can result in significant differences in total available surface moisture content.

Unfortunately, the moisture content is typically in the range of greatest dissimilarity when it is desirable to powder coat the wood substrate in question.

The unreliably uniform moisture content in the varying wood thickness has prevented the successful powder coating application of many material objects.

This problem is a major inhibitor to the future success of powder coatings on many non-conductive wood products.

Powder processing system designs currently adhere to the "separate equipment" mentality, and are burdened with unfavorable time lags between the heat processes and the application of the powder material to the substrate.

This is due to the significant distances that the parts in process must travel between separate pieces of processing equipment.

However, the substrate experiences a rapid surface temperature drop during its travel through time and space before the powder is actually applied.

This procedure causes a variety of problems for maintaining uniformity of temperatures over the substrate surface.

It can also cause an undesirable depletion of moisture, as well as the expulsion of natural wood resins (sap), from some substrates.

This is true because the absorption ability of IR radiation by the wood surface is high, but its thermal conductivity is considered to be very low.

However, this condition of uniformity will not remain for long periods of time, especially when the substrate must travel a significant distance through space and time to the powder spray application.

It should be noted that the atmosphere, including the chilled (or warm) moisture controlled fluid, does not efficiently absorb IR radiation.

Radiant losses from the heated surface typically exceed convective losses at elevated temperatures, such as 225.degree. F.

This radiant energy loss rapidly decreases the surface temperature of the interface area of the wooden part in process.

Lengthy travel time to separate processing equipment allows for a rapid decline of surface temperature because of the combination of radiant, convective...

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